Perfluorinated ion exchange polymers with pendant sulfonic acid groups have been used in a wide variety of acid catalyzed reactions, including hydrocarbon conversion reactions such as acylation, carbonylation, condensation, alkylation and oligomerization. For a review, see Waller et al., Chemtech, Jul., 1987, pp 438-441, and references therein.
In these acid catalyzed reactions, the perfluorinated ion exchange polymers with sulfonic acid groups have been used in the form of powders, films, cubes, flakes and tubes. In general, the catalytic efficiency (amount of product divided by the amount of catalyst) of such polymers is related to surface area, so that the powders of polymers show higher activity than cubes in non-swelling solvents. However, fine particulate particles tend to exhibit poor flow dynamics and lead to plugging problems and loss of catalyst due to entrainment. Films and flakes are inconvenient forms to use in many large scale industrial processes. Perfluorinated ion exchange polymers containing sulfonic acid groups in the form of tubing have only a moderate surface area to weight ratio and are fragile and difficult to manufacture.
Perfluorinated ion exchange polymers with pendant sulfonic acid groups have also been coated on various supports to increase the number of acid sites available, providing catalysts with increased catalytic efficiency at a lower cost.
U.S. Pat. No. 4,661,411 discloses the preparation of a heterogeneous acid catalyst, which involves treating a carrier material with a solution, which contains a fluorinated polymer dissolved in a suitable solvent, such polymer having sulfonic acid functional groups; removing the solvent involved in the prior step; and heat treating or annealing the coated carrier in a fashion to prevent the polymer from being leached from the carrier. Aqueous ethanol, particularly 50% aqueous ethanol used at 250.degree. C. or higher for several hours in an autoclave, is a suitable solvent for dissolving the unannealed fluorinated polymer. The composition of the carrier is not considered critical, and several, including carbon are suggested.
U.S. Pat. No. 4,038,213 discloses the preparation of a supported perfluorinated polymer catalyst by dissolving the polymer (a perfluorinated ion exchange polymer containing pendent sulfonic acid groups) in a solvent, such as ethanol, mixing the support and the catalyst solution, and then drying the impregnated support under vacuum. Disclosed supports or carriers have an average pore diameter of 50 to 600 .ANG. and are inorganic oxides such as alumina, fluorided alumina, zirconia, silica, silica-alumina, magnesia, chromia, boria, and mixtures thereof; other suitable porous supports include bauxite, kieselguhr, kaolin, bentonite, diatomaceous earth, polytetrafluoroethylene, carbon (e.g., charcoal), polytrichlorofluoroethylene and porous glass. The supported catalyst is useful in hydrocarbon conversion reactions, e.g., alkylation of isoparaffins, isomerization of normal alkanes, disproportionation of toluene and the alkylation of benzene.
U.S. Pat. No. 4,303,551 discloses an improved process for making supported perfluorosulfonic acid catalyst, comprising converting the sulfonic acid groups to the quaternary ammonium or phosphonium salts to effect solubility of the polymers, depositing the polymer containing the quaternary ammonium or phosphonium salts on a support, then, converting the ammonium or phosphonium salts to the sulfonic acid. The ammonium or phosphonium salts are soluble in dipolar, aprotic solvents such as dimethylformamide and dimethyl sulfoxide. A process is also disclosed for preparing a supported perfluorocarbon polymer containing pendant acid groups by first coating the support with a thin film of a catalyst precursor containing pendant groups which are convertible to acid groups, and then converting only the surface layer of said pendant groups into acid groups. Suggested supports include metal, Teflon.RTM. fibers, asbestos, glass, ceramics, sulfonyl fluoride polymers, and the perfluorocarbon sulfonyl fluoride itself.
In general, the supports have been chosen for their low cost, high surface area, inertness under the reaction conditions, mechanical strength or a combination of these factors. Little consideration has been given to the effect of the hydrophilic/hydrophobic nature of the support surface on the catalytic activity of the supported catalyst.
Quite unexpectedly, it has been found that catalysts obtained by coating perfluorinated ion exchange polymers with pendant sulfonic acid groups on supports with hydrophobic surfaces are significantly more active in acid-catalyzed reactions than similar catalysts prepared from supports with hydrophilic surfaces.